Hello,
Apparently a dump of PHM Pegasus Advanced Battle Disk can't be found. Surely It isn't present in the GB64 database. It's should be a extra scenario disk for PHM Pegasus (which is two side game: Side A: Boot, Side B: scenario).
Here an image of the disk: https://i.postimg.cc/XJpRCQQz/commodore ... 08e6c8.jpg